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Robert F Cooper, William Scott Tuten, Alfredo Dubra, David H Brainard, Jessica Ijams Wolfing Morgan; Spectral sensitivity of the cone photoreceptor intrinsic reflectance response. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3432. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Adaptive optics (AO) videos of the human cone mosaic have shown that visible light stimuli induce changes in infrared reflectivity. We have recently demonstrated that this infrared reflectance response is irradiance-dependent, suggesting a causal link between intrinsic reflectance and cone function. Such a link predicts that the spectral sensitivity of the reflectance response should approximately follow the luminous efficiency function. Here, we test this prediction.
Five subjects were imaged using an AO scanning light ophthalmoscope. After 2 minutes of dark adaptation, 1x1° videos were obtained 0.6° from the fovea using a 790nm imaging light. Four seconds after the start of each video a 2 second stimulus of varying wavelength and irradiance was delivered to half of the imaging raster. Temporal reflectance signals were extracted at each cone location and standardized to their pre-stimulus values. The standard deviation (SD) of reflectance was calculated separately for the stimulated and unstimulated cones at each time point, and the unstimulated SD was subtracted from the stimulated SD to obtain the reflectance response. For each subject, responses were measured at 2 wavelengths (550 and 510nm) and 4 retinal irradiances per wavelength (390, 140, 17 and 2nW/degree2). These data were combined with previously reported data for the same subjects/procedures, obtained using a 675nm stimulus with luminosity-matched irradiances. From these data, response amplitude versus irradiance plots at each of the three wavelengths were used to estimate the irradiance needed to obtain a criterion peak amplitude. These irradiances were normalized by the value for 550nm and inverted, providing a relative spectral sensitivity at 510 and 675nm. These were compared to the corresponding values from the CIE luminous efficiency function.
A wavelength and intensity-dependent intrinsic reflectance response was observed in all subjects. The mean spectral sensitivities obtained for 510 and 675nm were 0.56 (range: 0.23-0.85) and 0.034 (range: 0.007-0.067), respectively, in agreement with predictions from the luminous efficiency function at the same wavelengths (510nm: 0.52, 675nm: 0.03).
The measured spectral sensitivity of the cone intrinsic reflectance response approximated the luminous efficiency function, consistent with a link between the response and photopigment isomerizations.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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